High Fat Diet (HFD)-induced obesity is a major contributor to diabetes and cardiovascular disease, but the underlying genetic mechanisms are poorly understood. Here, we use Drosophila to test the hypothesis that HFD-induced obesity and associated cardiac complications have early evolutionary origins involving nutrient-sensing signal transduction pathways. We find that HFD-fed flies exhibit increased triglyceride (TG) fat and alterations in insulin/glucose homeostasis, similar to mammalian responses. A HFD also causes cardiac lipid accumulation, reduced cardiac contractility, conduction blocks and severe structural pathologies, reminiscent of diabetic cardiomyopathies. Remarkably, these metabolic and cardiotoxic phenotypes elicited by HFD are blocked by inhibiting insulin-TOR signaling. Remarkably, reducing insulin-TOR activity by TSC1-2, 4EBP, FOXO) or increasing lipase expression in the myocardium suffices to efficiently alleviate cardiac fat accumulation and dysfunction induced by HFD. We conclude that deregulation of insulin-TOR signaling due to a HFD is responsible for mediating the detrimental effects on metabolism and heart function.

SUMMARY Obesity and metabolic syndrome are associated with an increased risk for lipotoxic cardiomyopathy, which is strongly correlated with excessive accumulation of lipids in the heart. Obesity- and type 2 diabetes-related disorders have been linked to altered expression of the transcriptional cofactor PGC-1α, which regulates the expression of genes involved in energy metabolism. Using Drosophila, we identify PGC-1/spargel (PGC-1/srl) as a key antagonist of high-fat diet (HFD)-induced lipotoxic cardiomyopathy. We find that HFD-induced lipid accumulation and cardiac dysfunction are mimicked by reduced PGC-1/srl function and reversed by PGC-1/srl overexpression. Moreover, HFD feeding lowers PGC-1/srl expression by elevating TOR signaling and inhibiting expression of the Drosophila adipocyte triglyceride lipase (ATGL, Brummer), both of which function as upstream modulators of PGC-1/srl. The lipogenic transcription factor SREBP also contributes to HFD-induced cardiac lipotoxicity, likely in parallel with PGC-1/srl. These results suggest a regulatory network of key metabolic genes that modulates lipotoxic heart dysfunction.

The transcription factor dMyc is the sole Drosophila ortholog of the vertebrate c-myc protooncogenes and a central regulator of growth and cell-cycle progression during normal development. We have investigated the molecular basis of dMyc function by analyzing its interaction with the putative transcriptional cofactors Tip48͞Reptin (Rept) and Tip49͞Pontin (Pont). We demonstrate that Rept and Pont have conserved their ability to bind to Myc during evolution. All three proteins are required for tissue growth in vivo, because mitotic clones mutant for either dmyc, pont, or rept suffer from cell competition. Most importantly, pont shows a strong dominant genetic interaction with dmyc that is manifested in the duration of development, rates of survival and size of the adult animal and, in particular, of the eye. The molecular basis for these effects may be found in the repression of certain target genes, such as mfas, by dMyc:Pont complexes. These findings indicate that dMyc:Pont complexes play an essential role in the control of cellular growth and proliferation during normal development.repression ͉ transcription M yc proteins are essential regulators of growth, proliferation, and apoptosis in metazoans (1-3). These proteins act as transcription factors to control the expression of numerous target genes involved in growth, metabolism, and other processes (4-7). Less is known about the molecular mechanism that allows Myc to control the expression of these targets. In recent years, different modes of gene activation by Myc have been proposed, notably recruitment of chromatin remodelers (8), histone acetylases (e.g., ref. 9), or RNA pol II kinases (10), but the physiological relevance of these different factors for Myc-dependent biological functions needs to be demonstrated. We therefore set out to study the mechanisms of Myc-controlled growth and proliferation during normal development by using Drosophila as a model system. Initially, we focused on the interaction of Myc with two specific components of cofactor complexes, Tip48 and Tip49, because of the availability of null mutations in the corresponding genes [called reptin (rept) and pontin (pont) in flies, respectively].Tip48 and Tip49 are closely related proteins that show a high similarity to the bacterial ATP-dependent AAAϩ super family DNA helicase RuvB. Orthologs of Tip48 and Tip49 have been identified in plants, yeast, and animals (e.g., refs. 11 and 12). Different observations strongly suggest that one major function of the Tip proteins resides in the control of transcription. Initially, vertebrate Tip49 was found to be a Tata-binding protein-interacting protein (13-16); later Tip48 and Tip49 were also shown to interact physically with the different transcription factors ␤-catenin (11, 14), c-Myc (12), E2F1 (only Tip49) (17), and ATF2 (only Tip48) (18), raising the possibility that the Tip proteins could bridge basic transcription machinery and sequence-specific activators. Both proteins were also purified as part of several multiprotein complexes involved i...

Obesity has dramatically increased in prevalence, making it essential to understand its accompanying metabolic changes. Modeling diet-induced obesity in Drosophila melanogaster (fruit flies), we elucidated transcriptional and metabolic changes in w1118 flies on a high-fat diet (HFD). Mass spectrometry-based metabolomics revealed altered fatty acid, amino acid, and carbohydrate metabolism with HFD. Microarray analysis uncovered transcriptional changes in nitrogen metabolism, including CG9510, homolog of human argininosuccinate lyase (ASL). CG9510 knockdown in flies phenocopied traits observed with HFD, namely increased triglyceride levels and decreased cold tolerance. Restoration of CG9510 expression ameliorated observed negative consequences of HFD. Metabolomic analysis of CG9510 knockdown flies confirmed functional similarity to ASL, regulating the balance of carbon and nitrogen metabolism. In summary, we found that HFD suppresses CG9510 expression, a gene required for proper triglyceride storage and stress tolerance. These results draw an important link between regulation of amino acid metabolism and the response to diet-induced obesity.

SUMMARY Cardiac performance decreases with age, which is a major risk factor for cardiovascular disease and mortality in the aging human population, but the molecular mechanisms underlying cardiac aging are still poorly understood. Investigating the role of Integrin-Linked Kinase (ilk) and β1-Integrin (myospheroid, mys) in Drosophila, which co-localize near cardiomyocyte contacts and Z-bands, we find that reduced ilk or mys function prevents the typical changes of cardiac aging seen in wildtype, such as arrhythmias. In particular, the characteristic increase in cardiac arrhythmias with age is prevented in ilk and mys heterozygous flies with nearly identical genetic background, and they live longer, in line with previous findings in C. elegans for ilk and Drosophila for mys. Consistent with these findings we observed elevated β1-integrin protein levels in old compared to young wild-type flies, and cardiac-specific overexpression of mys in young flies causes aging-like heart dysfunction. Moreover, moderate cardiac-specific knockdown of integrin/ILK pathway-associated genes also prevented the decline in cardiac performance with age. In contrast, strong cardiac knockdown of ilk or ILK-associated genes can severely compromise cardiac integrity, including cardiomyocyte adhesion and overall heart function. These data suggest that mys/ilk function is necessary for establishing and maintaining normal heart structure and function, and appropriate fine-tuning of this pathway can retard the age-dependent decline in cardiac performance, and extend lifespan. Thus, integrin/ILK-associated signaling emerges as an important and conserved genetic mechanism in longevity, and as a new means to improve age-dependent cardiac performance, in addition to its vital role in maintaining cardiac integrity.

Pontin (Pont) and Reptin (Rept) are paralogous ATPases that are evolutionarily conserved from yeast to human. They are recruited in multiprotein complexes that function in various aspects of DNA metabolism. They are essential for viability and have antagonistic roles in tissue growth, cell signalling and regulation of the tumour metastasis suppressor gene, KAI1, indicating that the balance of Pont and Rept regulates epigenetic programmes critical for development and cancer progression. Here, we describe Pont and Rept as antagonistic mediators of Drosophila Hox gene transcription, functioning with Polycomb group (PcG) and Trithorax group proteins to maintain correct patterns of expression. We show that Rept is a component of the PRC1 PcG complex, whereas Pont purifies with the Brahma complex. Furthermore, the enzymatic functions of Rept and Pont are indispensable for maintaining Hox gene expression states, highlighting the importance of these two antagonistic factors in transcriptional output.

Obesity is strongly correlated with lipotoxic cardiomyopathy, heart failure and thus mortality. The incidence of obesity has reached alarming proportions worldwide, and increasing evidence suggests that the parents’ nutritional status may predispose their offspring to lipotoxic cardiomyopathy. However, to date, mechanisms underlying intergenerational heart disease risks have yet to be elucidated. Here we report that cardiac dysfunction induced by high-fat-diet (HFD) persists for two subsequent generations in Drosophila and is associated with reduced expression of two key metabolic regulators, adipose triglyceride lipase (ATGL/bmm) and transcriptional cofactor PGC-1. We provide evidence that targeted expression of ATGL/bmm in the offspring of HFD-fed parents protects them, and the subsequent generation, from cardio-lipotoxicity. Furthermore, we find that intergenerational inheritance of lipotoxic cardiomyopathy correlates with elevated systemic H3K27 trimethylation. Lowering H3K27 trimethylation genetically or pharmacologically in the offspring of HFD-fed parents prevents cardiac pathology. This suggests that metabolic homeostasis is epigenetically regulated across generations.

The high degree of genetic conservation between Drosophila melanogaster and mammals has helped to translate many important findings into new knowledge, and has led to better understanding of many biological processes in vertebrates. For over a century, the Drosophila model has been used in studies aimed at understanding molecular mechanisms implicated in heredity, development, disease progression, and aging. The current epidemic of obesity and associated diabetic cardiomyopathy and heart failure has led to a shift in Drosophila research towards understanding the basic mechanisms leading to metabolic syndrome and associated cardiac risk factors. Here, we discuss recent findings in Drosophila that highlight the importance of this organism as an excellent model to study the effects of metabolic imbalance on cardiac function.